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This dome on the roof will be the planetarium. Work crews are in the final months of construction on the California Academy of Sciences in Golden Gate Park where the roof will be covered with a garden of California native plants. Photographed in San Francisco on 5/10/07. Deanne Fitzmaurice / The Chronicle Mandatory credit for photographer and San Francisco Chronicle. No Sales/Magazines out.

Photo: Deanne Fitzmaurice

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This dome on the roof will be the planetarium....

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Beach strawberries are one of the plants which will be planted on the rooftop. Work crews are in the final months of construction on the California Academy of Sciences in Golden Gate Park where the roof will be covered with a garden of California native plants. Photographed in San Francisco on 5/10/07. Deanne Fitzmaurice / The Chronicle Mandatory credit for photographer and San Francisco Chronicle. No Sales/Magazines out.

Photo: Deanne Fitzmaurice

roof13_055_df.jpg
Beach strawberries are one of the plants which...

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Cooper Scollan, the nursery manager holds a tray of perennials planted in a BioTray, made of biodegradable coconuts.
Work crews are in the final months of construction on a state of the art museum complex for the California Academy of Sciences in Golden Gate Park. One of the most remarkable parts of the project is taking shape 125 miles to the south, at Rana Creek Living Architecture, a plant nursery in Carmel Valley, where 1.7 million native California plants are being grown for a 2.5 acre living roof atop the science center. Photo taken on Wednesday May 9, 2007.
Photo by Michael Maloney / San Francisco Chronicle *** Cooper Scollan MANDATORY CREDIT FOR PHOTOG AND SF CHRONICLE/NO SALES-MAGS OUT

Photo: Michael Maloney

Cooper Scollan, the nursery manager holds a tray of perennials...

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A self-sustaining, colorful top to the new California Academy of Sciences. Chronicle graphic by Joe Shoulak

A self-sustaining, colorful top to the new California Academy of...

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How the Rooftop Works. Chronicle graphic by Joe Shoulak

How the Rooftop Works. Chronicle graphic by Joe Shoulak

A GARDEN IN THE SKY / S.F. museum's roof puts green building techniques to the test

Work crews are about to start planting the roof of the new California Academy of Sciences museum in Golden Gate Park -- an architectural capstone that also qualifies as one of the world's most ambitious biodiversity experiments.

Roof gardens are as ancient as Babylon and a deeply rooted fad in Europe, but the vegetated structure taking shape in the park is perhaps the grandest foray yet into what museum visionaries like to call "integrated regenerative architecture."

Gregory Farrington, the new executive director of the California Academy, views the roof as a unique scientific showplace designed to flip the conventional museum concept on its head.

"Most museums have thick walls that separate the inside from the outside and put in the basement or on the roof all the systems that you need to make the place functional. Here, the idea will be to make the building itself into an exhibit, and there is no separation of the inside from the outside," he said.

Visitors to the $300 million science center who make their way up to a rooftop viewing platform after the museum opens next year will see none of the hulking ventilation towers and emergency generators that cap most big buildings.

Those things and other utility systems have been buried underground to make way for 197,000 square feet of native strawberries, stonecrop and California poppies.

The pioneer plants are growing now in neat rows of portable "biotrays" -- 17-inch-square containers of biodegradable coconut husk woven in the Philippines -- at the Rana Creek Wholesale Nursery, specialists in West Coast native species, in Carmel Valley, 125 miles south of the construction site.

Barring any last-minute construction delays, the biotrays will be trucked to the park starting May 23 and fitted into place one by one, like 3-inch-deep cake pans, on top of a complicated multilayered substrate that forms the roof's living skin.

In size and design, the academy roof is unprecedented, marked by seven domes and steep hillocks envisioned by celebrity lead architect Renzo Piano as a nod to San Francisco's undulating topography.

The hills allow space inside for the museum's planetarium and the sky-lit dome of a rain forest display. But the idea is to draw attention outside to the rooftop forest of native plants, an estimated 1.7 million individuals representing four perennial and five wildflower species.

The plants will be the museum's first living residents, in effect expanding the greenswards of Golden Gate Park by 2 1/2 acres. But designers insist the project is more about philosophy than botany.

The building's green crown is intended to push the idea of urban sustainability in the era of global warming. In that sense, the roof is a symbol of "the need for a general consciousness shift by our culture," said Paul Kephart, executive director at Rana Creek, who is serving as a project design consultant.

"We are, in fact, responsible for climate change and impacts on biodiversity. Now we're taking action on those things," he said.

If such notions as a "green economy" and "living architecture" thrive as the visionaries hope, green roofs should be sprouting all over. In fact, that already is happening in the form of such other notable projects as the convention center in Vancouver, British Columbia, and the Gap headquarters in San Bruno.

California Academy patrons will still get to see the classic dioramas, fish tanks and live alligators that made the old natural history museum a popular destination in Golden Gate Park. The roof of the new structure adds a functional outdoor element, weaving the museum into ecosystems as well as tourist maps and guidebooks.

Engineers expect the roof to serve a working role for the building by attenuating sound and reducing storm water runoff. Its many skylights, and a retractable ceiling over a central piazza, will draw in sunlight and circulating air.

It even will keep rain off people's heads.

Equally important, the roof's plants were specially chosen to create habitat for the endangered bay checkerspot butterfly, draw bumblebees and hummingbirds, and maybe serve as a camping spot for migratory West Coast bird life.

Last week, Cooper Scollan, nursery manager at Rana Creek, stepped around a shrieking killdeer feigning a broken wing that had lain three eggs among the armeria and prunella at the nursery, soon to be relocated to Golden Gate Park. A work crew methodically moved along the rows of biotrays, removing weeds and planting new seedlings.

Scollan and colleagues collected many of the starting plants and seed stock from private landowners around the Bay Area. The nine plant types, including annual wildflowers not yet seeded, emerged from field testing of about 30 species as the most likely to endure on the roof with minimal or no watering after an initial break-in period.

At Golden Gate Park, meanwhile, academy botany chief Frank Almeda took visitors for one of the final looks around the still-naked rooftop last week. A thick sandwich is now being built up to welcome the plants, including layers for insulation, waterproofing and drainage, plus 3 inches of soil mix beneath the coconut husk.

It's costing about $17 a square foot. No one can predict how all the plants will fare, and there's a chance many problems will crop up, including the possibility of a quick takeover by the fast-spreading beach strawberries.

Almeda said he was confident the roof will be healthy and plenty green by the time the museum completes its elaborate move-in and officially opens, scheduled for October 2008, even if the current dry spell deepens into drought.

-- Collection of 20 million scientific specimens dating back to the Academy's founding in 1853

-- Naturalist center and classrooms

A self-sustaining, colorful top to the new California Academy of Sciences

Roof with a view

The 2.5-acre "green roof" will be planted with native California species to provide habitat for birds and butterflies while also serving as an exhibit on environmental sustainability and biodiversity. An elevator will carry visitors up to the roof viewing deck.

The rooftop features solar panels arrayed in a 30-foot canopy.

Circular skylights will provide light and vent heat from inside.

A central square on the rooftop will open to the piazza below.

What's underneath the plants

Fifty thousand biodegradable coconut husk trays will be placed throughout the rooftop. Each tray will contain the nine chosen plant species at right.

Growing medium (organic and inorganic material)

Filter sheet (prevents soil from washing into drainage)

Drainage layer (strong lightweight plastic)

Root barrier (prevents roots from going into concrete ceiling)

Waterproofing (thermal plastic membrane)

The selected nine plant species

Over 30 species were tested on the roof of the old Academy before demolition began in 2004.

Above: Self heal (Prunella vulgaris).

At right: A common checkerspot butterfly extracts nectar from a beach strawberry blossom (Fragaria chiloensis).

Multilayered roof surface protects the building from the elements and serves as a substrate for the native plants. The design is intended to enhance water and energy conservation while also blending into the park setting.

Heat from the sun vents out throughout the piazza and via skylights on the rooftop.

The roof is designed to collect rainwater for use as gray wastewater throughout the building.

The shape of the rounded hills on the rooftop was designed to draw cool air into the piazza.

Aquarium tanks will use saltwater piped in from the Pacific Ocean as it was in the former facility. However, natural systems will be used to purify wastes, ensuring that aquarium water can be recycled.

The new building will have a smaller footprint returning more than one acre of green space to Golden Gate Park.